1. Field of the Invention
The present invention relates to a vehicle and a method for controlling the vehicle, and more particularly, to control of a vehicle including a belt-type continuously variable transmission.
2. Description of the Related Art
Conventionally, a belt-type continuously variable transmission mounted on a vehicle such as a saddle-riding type vehicle includes one in which the interval between sheaves for sandwiching a belt is changed by an actuator. In a vehicle equipped with a belt-type continuously variable transmission, the belt may likely slip relative to the sheaves upon sudden torque fluctuation occurring at the drive wheel due to running on a bad conditioned road. Such slip of the belt is not preferable in view of durability of the belt and the sheaves.
According to a technique disclosed in Japanese Patent Laid-open Publication No. 2003-269591, in order to prevent slip of the belt, a force for clamping the belt with the sheaves (hereinafter referred to as a clamping force) is increased when the rotation speed of the drive wheel is changed. However, even though the actuator is activated after detection of change in the rotation speed of the drive wheel, torque fluctuation may likely have been transmitted to the continuously variable transmission by the increase of the clamping force.
Moreover, according to another technique disclosed in Japanese Patent Laid-open Publication No. 2003-269591, the clamping force is increased upon estimation, based on a value obtained in integration with an amount of change in the rotation speed of the drive wheel, to the effect that the road on which the vehicle is running is in a bad condition. However, as the clamping force is kept increasing even though the torque fluctuation occurring is relatively so small that slip of the belt will not be caused, torque transmission efficiency of the continuously variable transmission may be deteriorated.